This section introduces aspects that may help to facilitate a better understanding of the invention(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
Pseudowires (PWs) are deployed in the packet switch network (PSN) because it allows a service provider to extend the reach of Pseudowire (PW) across multiple domains. These pseudowires are called multi-segment pseudowires (MS-PWs). These domains can be autonomous systems under one provider administrative control, Interior Gateway Protocol (IGP) areas in one autonomous system, different autonomous systems under the administrative control of two or more service providers, or administratively established pseudowire domains. In reference 1, N. Bitar, Ed., “Requirements for Multi-Segment Pseudowire Emulation Edge-to-Edge (PWE3)”, RFC5254, Oct. 2008, architecture and use cases of MS-PW have been discussed.
The solution of MS-PW resiliency should allow for the protection of a PW segment, a contiguous set of PW segments, as well as the end-to-end path. Reference 1 has also discussed the requirements for MS-PW resiliency.
The most used solution is the protection of end-to-end path. The protection entity is deployed in the terminating-provider edge (T-PE) node.
In some MS-PW scenario, there are some benefits to provide PW redundancy on switching-provider edge (S-PE) node, such as reducing the burden on the access T-PE nodes, and faster protection switching. In reference 2, J. Dong, and H. Wang, “Pseudowire Redundancy on S-PE”, draft-dong-pwe3-redundancy-spe-04, Nov. 22, 2012, some scenarios in which PW redundancy is provided on S-PEs are described, and the operations of the S-PEs are specified.
FIG. 1 shows the MS-PW redundancy on S-PE with S-PE protection. Terminating provider edges T-PE1 and T-PE2/T-PE3 provide PW Emulation Edge-to-Edge service to customer edges CE1 and CE2. These PEs may reside in different PSN or pseudowire domains. PWs are used to connect the Attachment circuits (ACs) attached to T-PE1 to the corresponding ACs attached to T-PE2 and T-PE3. Each PW on a PSN tunnel is switched to a PW in the tunnel at switching provider edges S-PE1/S-PE2 to complete the MS-PW between T-PE1 and T-PE2/T-PE3. S-PE1/S-PE2 is therefore the PW switching point. An S-PE switches an MS-PW from one segment to another based on the PW identifiers.
As illustrated in FIG. 1, CE1 is connected to T-PE1 while CE2 is dual-homed to T-PE2 and T-PE3. T-PE1 is connected to S-PE1 and S-PE2, and both S-PE1 and S-PE2 are connected to T-PE2 and T-PE3. There are two MS-PWs which are switched at S-PE1 and S-PE2 respectively to provide S-PE node protection. For MS-PW1, the S-PE1 provides resiliency using PW1-Seg2 and PW1-Seg3. For MS-PW2, the S-PE2 provides resiliency using PW2-Seg2 and PW2-Seg3. MS-PW1 is the working PW and PW1-Seg2 is the working PW segment.
However, both solutions have the following limitations. First, one PW failure within one PSN will trigger the switchover behaviour within other PSNs. It is not preferred if they are administrated by different operators. Second, one failure in AC link may trigger multiple switching behaviours in PSN domains. For example, in FIG. 1, the interface between T-PE2/T-PE3 and CE2 are Synchronous Transport Module level-1 (STM-1). Multi-chassis Automatic Protection Switching (MC-APS) or Multiplex Section Protection (MSP) is deployed in T-PE2 and T-PE3. One failure in AC link (between T-PE2 and CE2) will cause the switching behaviour in up to 63 PW instances if Structure-Agnostic Time Division Multiplexing (TDM) over Packet (SAToP) is deployed and one PW can only hold one E-carrier (E1) traffic.
Except mentioned above, the protection of end-to-end path further has the following drawbacks. Protection switching may be slower in some scenarios. The failure notification should be transmitted to the T-PEs. Then T-PEs can negotiate each other to perform the switching. The path may be long in some cases. It will result in the slow protection switching.